The Great Cave Offensive

In Kirby Super Star, The Great Cave Offensive was a sub-game where Kirby, well, explored a great cave. After falling into a hole while taking a walk, he scoured the labyrinthine cave looking for treasures, fighting many unique bosses - from a giant rocky golem and a goofy chameleon to a massive whale and a turn-based RPG computer virus. Interestingly, many concepts from The Great Cave Offensive, such as save rooms and branching pathways, were used in Super Smash Bros. Brawl's Subspace Emissary mode.